Aggregators like this can't control their own destiny until they become their own content platform. While navigating the long road to become a platform, they're at the mercy of changing API policies and rate limits of the different content platforms.
Instagram can decide at anytime to shut off access or remove an endpoint which will greatly reduce the user's experience.
It's also tough to build a unified AI to engage with so many different types of content. Most people will be familiar with the the UIs of the respective platforms which are already tuned toward content consumption. I do grant those UIs may not have the user's best interests in mind as they focus on hitting engagement and retention KPIs.
It is an interesting one though, almost an "adblock for over-optimized UIs".
They may be able to find something that works for a niche group of creatives if they can manage the challenges above.